Capacitive touchpad is used as an input device to control cursor movement by providing a smooth panel for user's finger or conductive object to touch or move thereon. Since a capacitive touchpad is very thin, it can be designed into an ultra-thin notebook, a keyboard, a digital player and other devices, and further, its non-mechanical design makes it very easy to be maintained.
FIG. 1 shows a cross-sectional view of a typical two-dimensional capacitive touchpad 100, which comprises a panel 102, a Y-axis sensing layer 104, an insulator layer 106, an X-axis sensing layer 108, and a bottom plate 110. When a finger 112 touches on the panel 102, the sensed value on the touched position will have a variation, and the control circuit connected to the touchpad 100 can convert the capacitances on the touchpad 100 to the sensed value as shown in FIG. 2, by which the position where the finger 112 touches and the moving distance and the moving direction of the finger 112 can be determined. Conventionally, the sensed value from the touchpad 100 is used to determine if an object touches on the touchpad 100 by the way as shown in FIG. 3. When the sensed value is greater than a threshold value th, it is determined that an object touches on the touchpad 100; on the contrary, when the sensed value is less than the threshold value th, it is determined that the object leaves the touchpad 100 or no object touches on the touchpad 100.
However, the way to operate programs or devices by detecting gestures of single object, such as touching down to a touchpad, leaving from a touchpad, and moving on a touchpad, could no longer fulfill users' requirements in current electronic products. For this reason, there is a need to detect double or even more objects on a touchpad. Specifically, the actions of multiple objects operating on a touchpad can be defined as various gestures to vary the operations.
There have been proposed several detection methods for multiple objects touching on a touchpad. For example, in U.S. Pat. No. 5,825,352 issued to Stephen et al., the waveform of sensed values is detected to determine the object touching on a touchpad. FIGS. 4A to 4D show the waveforms of sensed values from a touchpad 001 in two directions in a conventional method. In FIGS. 4A to 4D, X profile 002 is the distribution of the sensed values in the horizontal direction of the touchpad 001, and Y profile 003 is the distribution of the sensed values in the vertical direction of the touchpad 001. Each peak of the waveform in the X profile 002 represents an object touching on the touchpad 001. For example, as shown in FIG. 4A, the waveform in the X profile 002 has single peak 021, and it means there is only one object 011 on the touchpad 001. In FIG. 4B, the waveform in the X profile 002 has two peaks 021 and 022, and it means there are two objects 011 and 012 on the touchpad 001. As shown in FIG. 4C, if the waveform in the X profile 002 has three peaks 021, 022, and 023, it means there are three objects 011, 012, and 013 on the touchpad 001. By detecting the number of the objects on the touchpad 001, various gestures could be identified. For instance, two objects moving on the touchpad 001 may be defined as a first gesture, and two objects leaving from the touchpad 001 within a reference time interval since their touching down to the touchpad 001 may be defined as a second gesture, and so on. By this way, practical gestures are increased and the operations become more simple and varied.
However, it cannot determine the respective movements of two or more objects by the foregoing method. For example, as shown in FIG. 4B, two objects 011 and 012 touches on the touchpad 001, resulting in the X profile 002 having two peaks 021 and 022 and the Y profile 002 having one peak 031. Then, if the object 011 starts to move upward and the object 012 keeps still on the touchpad 001, the X profile 002 still has two peaks 021 and 022, while the Y profile 003 splits from one peak 031 to two peaks 031 and 032 as shown in FIG. 4D. It becomes more difficult to determine which object on the touchpad 001 is the moved one. If the movement of respective object can be determined individually, more practical gestures can be defined, and more operations for a touchpad can be applied thereto.
Therefore, it is desired a method for detecting the movement of respective one among multiple objects on a capacitive touchpad.